1. Technical Field
The present invention pertains to telecommunications, and particularly to Voice over Internet Protocol (VoIP).
2. Related Art and Other Considerations
Voice over Internet Protocol (VoIP) in the mobile world means using a packet switched (PS) service for transport of Internet Protocol (IP) packets (which contain, e.g., Adaptive Mutli-Rate codec (AMR) speech frames) for normal mobile phone calls. In circuit-switched networks, network resources are static from the sender to receiver before the start of the transfer, thus creating a “circuit”. The resources remain dedicated to the circuit during the entire transfer and the entire message follows the same path. In packet-switched networks, the message is broken into packets, each of which can take a different route to the destination where the packets are recompiled into the original message.
The packet switched (PS) service utilized for VoIP can be, for example, GPRS (General Packet Radio Service), EDGE (Enhanced Data Rates for Global Evolution), or WCDMA (Wideband Code Division Multiple Access). Each of these example services happen to be built upon the Global System for Mobile communications (GSM), a second generation (“2G”) digital radio access technology originally developed for Europe. GSM was enhanced in 2.5G to include technologies such as GPRS. The third generation (3G) comprises mobile telephone technologies covered by the International Telecommunications Union (ITU) IMT-2000 family. The Third Generation Partnership Project (3GPP) is a group of international standards bodies, operators, and vendors working toward standardizing WCDMA-based members of the IMT-2000.
EDGE (or Enhanced Data Rates for Global Evolution) is a 3G technology that delivers broadband-like data speeds to mobile devices. EDGE allows consumers to connect to the Internet and send and receive data, including digital images, web pages and photographs, three times faster than possible with an ordinary GSM/GPRS network. EDGE enables GSM operators to offer higher-speed mobile-data access, serve more mobile-data customers, and free up GSM network capacity to accommodate additional voice traffic.
EDGE provides three times the data capacity of GPRS. Using EDGE, operators can handle three times more subscribers than GPRS; triple their data rate per subscriber, or add extra capacity to their voice communications. EDGE uses the same TDMA (Time Division Multiple Access) frame structure, logic channel and 200 kHz carrier bandwidth as GSM networks, which allows existing cell plans to remain intact.
In EDGE technology, a base transceiver station (BTS) communicates with a mobile station (e.g., a cell phone, mobile terminal or the like, including computers such as laptops with mobile termination). The base transceiver station (BTS) typically has plural transceivers (TRX), with each transceiver having plural timeslots. Some of the transceivers (TRX) are capable of “hopping”, e.g., frequency hopping. Frequency hopping is a process in which the data signal is modulated with a narrowband carrier signal that “hops” in a random but predictable sequence from frequency to frequency as a function of time over a wide band of frequencies. In GSM a channel such as the broadcast control channel (BCCH) must (in practice) be on a non-hopping transceiver.
A typical GSM network cell configuration has one of the transceivers of a base transceiver station (BTS) configured as non-hopping, and puts the BCCH on the non-hopping transceiver. As the BCCH must be configured with a low frequency reuse, the whole transceiver gets a very good carrier to interference ratio C/I. The rest of the non-hopping transceiver (e.g., the remaining 6-7 timeslots of the non-hopping transceiver) can be configured (as available) for EDGE. These non-hopping transceiver timeslots will (thanks to the good C/I) provide very high bitrate, as the bitrate in EDGE varies depending on the C/I.
The other transceivers in the cell are typically configured as hopping and planned with a very tight reuse for maximum network capacity from the available frequency spectrum. These timeslots will (due to the lower C/I) provide much lower bitrate per timeslot since (as stated before) the bitrate in EDGE varies depending on C/I. FIG. 5 shows generally throughput (bitrate) as being a function of radio quality (C/I).
VoIP may be more hardware efficient than a circuit switched CS connection on the non-hopping transceiver with the BCCH. Such efficiency advantage is a result of the higher C/I for which the BCCH transmitter is frequency planned via, e.g., frequency reuse (e.g., greater distance between cells using the same frequency). For example, more users could be served on a same number of timeslots as compared to circuit switched connections. However, a significant problem can develop in that VoIP may be less hardware efficient than CS on the hopping TRXs as a result of the lower radio quality (C/I) of the hopping TRXsSo, while VoIP may be beneficial on one (non-hopping) transceiver of a base transceiver station (BTS), VoIP may not be beneficial on another (hopping) transceiver.
In the early or introductory days of VoIP, it is expected that many users will upgrade from an old circuit switched phone to a VoIP phone. It is likely that each such upgrading user will bring a benefit for the operator in terms of increased hardware efficiency. But eventually at a certain VoIP penetration, each user upgrading from an old circuit switched phone to a VoIP phone will bring a penalty to the operator in terms of decreased hardware efficiency.